1. Field of the Invention
The invention relates to benzoyl alanines and to the use thereof as corrosion inhibitors in aqueous systems.
2. Description of Prior Art
Corrosion problems quite often occur in numerous industrial processes where aqueous media comes into contact with metallic surfaces such as iron, copper, aluminum, zinc and the various alloys thereof. Examples of such processes are cleaning processes in which aqueous industrial cleaning solutions are used; cooling processes in which water-containing coolant systems are employed; and processes involving cooling and simultaneous lubrication in machining metals.
In published German Patent Application No. 11 49 843, the use of semi-amides of maleic acid or succinic acid are disclosed as useful as additives for fuel or lubricant oils. However, these compounds have one drawback since in most cases, they are not water-soluble and since homogeneous dispersion thereof in the process liquid cannot be assured.
The U.S. Pat. No. 4,207,285 also discloses semi-amides of maleic acid as corrosion inhibitors for aqueous systems. The alkyl groups attached to the amide nitrogen atom in such compounds contain from 9 to 12 carbon atoms. The resulting amide acids are neutralized with mono-, di- or trialkanol amides or mixtures thereof.
In addition, corrosion inhibitors which have been proposed for iron in alkaline media include alkenyl succinic acids (published German Patent Application No. 29 43 963; Chemical Abstracts 95: 101406d), long-chain sulfonamidocarboxylic acids (published German Patent Application No. 12 98 670; Chemical Abstracts 71: 72064n), acyl sarcosinates (Winnacker-Kuechler, Chemische Technologie, C.-Hanser-Verlag, Munich (1960), page 199) or alkali metal benzoates. In the past fatty amines or amidazolines have been used primarily for iron corrosion inhibition in weakly acidic media. However, fully satisfactory results were not attainable.
Alkali metal silicates or alkali metal benzoates have been used as corrosion inhibitors for aluminum in alkaline media. However, the results attained using such components have not been generally satisfactory. A particular disadvantage inherent in the use of those compounds is that they are effective only in very high concentrations.
The use of corrosion inhibitors of the type heretofore mentioned not only provides inadequate protection from corrosion but also causes a number of problems in their practical application. For example, undesired heavy foaming of the compounds occurs in aqueous solutions and poor water-solubility and/or poor stability to water hardness or inadequate stability during storage restricts greatly the practical utility of some of the aforementioned compounds. Additionally, attention has to be directed to the toxicity of the compounds which often is excessively high, and to their extremely poor biodegradability.
In U.S. patent application Ser. No. 713,123, filed Mar. 18, 1985, and incorporated herein by reference, the use of certain benzoyl alanines as corrosion inhibitors for aqueous systems is disclosed. The benzoyl alanines in question exhibit excellent anticorrosive properties as well as high water-solubility and low foaming characteristics. However, the compounds disclosed in said patent application are disadvantageous in that they are unduly sensitive to changes of the process water hardness and manifest a lack of sufficient temperature stability.